The present invention relates to a single acting semi-rotating fluid pressure actuator provided with return springs secured by a single end cap.
As is known, the rotary movement of the shutter of particular types of valves, for the opening and closure of such valves, can be advantageously derived from the movement of rotary actuators, generally actuators functioning by means of a fluid under pressure such as hydraulic or pneumatic actuators. Such actuators are essentially constituted by an hydraulic or pneumatic directly or indirectly driven semi-rotating motor. The term "semi-rotating" will be understood to refer to a member having a limited range of rotary movement, usually less than a complete revolution.
In particular, indirectly driven actuators of this type comprise two opposed pistons in a cylinder on which pistons the fluid under pressure acts and from which pistons the movement and the forces are transmitted to an output shaft by means of a rack and pinion coupling. The return stroke of the pistons themselves is usually obtained by means of the action of biasing springs.
This arrangement, whilst being advantageous for many purposes and whilst having great operating reliability, does however present certain practical difficulties of assembly and maintenance. In fact, assembly is difficult because after having assembled the pistons, the insertion and retaining of the springs in their associated seatings involves a laborious operation including compression of the springs to fit the sealing end caps given the diameters of the springs themselves and their consequent resistance to compression.
The complexity of such operations in practice renders in situ maintenance of the actuator impossible, therefore making it necessary first to remove it from its working position for any necessary maintenance operations such as exchange of the springs, changing the seals or internal cleaning in general etc. It is in fact dangerous, and practically impossible, to dismantle the end caps from actuators of conventional type having return springs unless suitable specialised tools are available such as, for example, locking vices and presses able to resist and contain the thrust action of a multiplicity of springs.
Moreover, in currently available spring return single acting actuators it is not possible to effect a correct adjustment of the load of the springs in relation to the control pressure and the resisting couple of a valve worked by the actuator, without replacing the springs themselves.